Embryology: Body Plan Flashcards
What are the three embryonic germ layers?
Ectoderm, mesoderm, and endoderm
What tissues arise from the ectoderm?
Central/peripheral nervous systems, some skeletal and connective tissue of the head, epidermis, hair, nails, sensory epithelium of nose/ear/eye
What tissues arise from the mesoderm?
Skeletal/smooth/cardiac muscle, cartilage, bone, connective tissue, blood, urogenital system
What tissues arise from the endoderm?
Epithelium of the gut and it’s derivatives, epithelium of the respiratory system
What is caudal regression syndrome?
A disorder of impaired development of the lower half of the body. Can include lower limbs, lower back (lumbar/sacral vertebrae), lower gut, and urogenital tracts.
What is the underlying mechanism of caudal regression syndrome?
Abnormal growth and migration during gastrulation resulting in abnormal development of the caudal mesoderm, which is the last mesoderm to form
What is sirenomelia?
An extreme and rare form of caudal dysplasia in which the two lower limbs are fused at the midline. GI and GU organs are often malformed or absent. Usually fatal.
What is embryonic induction?
The stimulation of a specific developmental pathway in one group of cells by a closely approximated second group of cells. The inducing tissue passes a signal to the responding tissue, which “changes the fate” of the responding tissue.
What are the three different mechanisms of embryonic induction?
Diffusion of the inducing molecule from inducing tissue to responding tissue; contact between the ECM of inducing and responding cells; direct contact between the inducing and responding cells
What are the four examples of embryonic induction that Dr. Hartley wants us to know?
Primitive streak formation, mesoderm formation, neural induction, and lens induction.
What is the mechanism of primitive streak formation?
Signaling from extra-embryonic tissue (via TGF-beta and Wnt family molecules) induces epiblast cells to form primitive streak
What is the mechanism of mesoderm formation?
FGF produced by the endoderm causes migrating epiblast cells to become mesoderm
What is the mechanism of neural induction?
Primitive node cells produce TGF-beta family antagonists, FGF/IGF family molecules, which causes the ectoderm to form the neural plate
What is the mechanism of lens induction?
The optic vesicle develops as an extension of the embryonic brain and produces BMP4 (TGF-beta family), causing the overlying ectoderm to differentiate into the lens instead of skin
What is the period of susceptibility and when does it occur?
The period when the embryo is most vulnerable to environmental factors causing abnormal development; weeks 4-8
Insults during which period usually result in spontaneous abortion?
First three weeks
What is an anomaly?
A marked deviation from “normal”
What is an association?
A nonrandom appearance of two or more anomalies together with an unknown cause
What is the definition of congenital?
Present at birth
What is a deformation?
A structural defect resulting from mechanical forces on the fetus over a prolonged period
What is a malformation?
A structural defect resulting from abnormal embryonic or fetal development
What is a sequence?
Multiple defects determined by a primary anomaly
What is a syndrome?
A group of anomalies occurring together that have a specific common cause
What is a teratogen?
An agent or factor that can disturb the development of an embryo
How long after fertilization does the blastocyst implant in the uterine wall?
About 1 week
What does the egg become after the development of the two pronuclei?
Zygote
What does the zygote become after it’s first mitotic division?
Blastomere
For how long is the blastomere totipotent?
Until 4-8 cell stage
What is the definition of totipotent?
Can give rise to both the embryo and the fetal part of the placenta
What does the blastomere become when it reaches the 16 cell stage?
Morula
What is the definition of pluripotent?
Can give rise to all cell types except the placenta
What two processes happen as the cells of the morula divide?
Compact (move closer together) and cavitate (secrete fluid to form a cavity)
What does the morula become after compaction and cavitation?
Blastocyst
How long does the implantation process take?
About a week (week 1-2)
What is the embryoblast?
The inner cell mass of the blastomere; forms the embryo
The embryoblast contains what type of stem cells?
Totiipotent
What is the trophoblast?
The outer cell mass of the blastomere; form the fetal part of the placenta
The trophoblast contains which type of stem cells?
Pluripotent
When do the blastomeres segregate into the embryoblast and the trophoblast?
Around day 6
When do the blastomeres segregate into the embryoblast and the trophoblast?
Around day 6
What two layers does the embryoblast differentiate into, and what cavities do they form?
Epiblast - columnar cells that secrete fluid to form the amniotic cavity; hypoblast - cuboidal cells migrate to line the blastocyst to form the primitive yolk sack
What is the embryo called when it forms two layers of the embryoblast?
Bilaminar embryo
What two layers does the trophoblast differentiate into, and what cavities do they form?
Syncytiotrophoblast - outer layer, one cell with many nuclei; cytotrophoblast - actively proliferating cells
